Preparation of sodium thiocarbonate



Patented Nov. 19, 1940 .No Drawing. A Application March 4, 1;.SerialNo.-259;794

PREPARATION oFfsoD THIOCARBON'ATE'H Sheldon l3. Heathand Wallis RirBennettr;

land, ;Mich.,: 3155151 918. to The B Company, Midland, Mich a. corp Thisinvention is concerned with anim-proved method for the preparationof-sodium'thiocarbonate and .a product thereby obtained. if

Sodium thiocarbonate-is a yellow, crystallin compound soluble in coldwater and-decomposed by hot water. This compound is commonly prepared byreacting-carbon bisulphide with sodium sulphide hydrate to obtain acrudeproduct: which has been found useful as aweed killer. A poten- .tial useof the compound as a component of in- .secticidal and antisepticcompositions andas a laboratory reagent requires that the compound beemployed in water solution. Aqueous fcompositions heretofore availablehave contained as "an impurity. sodium sulphide in amount equal tofromlO-toBO, per cent by weight of dissolved so- .dium thiocarbonateandsince sodium sulphide is an active tanning. agent andotherwise:objection,- able, it is desirable that some means be developed toprovide sodium thiocar-bonate solutions .substantially free of sodium.sulphidepcontamination. Among the objects of this invention are (1) toprovide a commercially feasible method whereby solutions ofsodiumthiocarbonate may. be pre- .pared which are substantiallyireeofsodium sulphide contamination, and (2). .rtoprovide. .a 'methodfor the preparation of ;sodium thiocar- 'bonate from carbon .bisulphide.and sodium. sul- -phide hydrate wherein the sodium sulphide hydrate issubstantially completelyreacted with the carbon bisulphide sothat. the.involved. procedure of separation of sodium thiocarbonate from. residualsodium sulphide is obviated.

According to .the invention, concentrated aqueous solutionssof sodiumthiocarbonate are-prepared containing less than 1 per 'cent by weight ofsodium sulphide on the basis of the .dissolved sodium thiocarbonate.This is-accomplished by partially reacting sodium sulphide hydrate witha molecular excess .of carbon bisulphide inthe presence of water,thereafter, adjusting the.pH of the reaction mixture to 8.0 orhigherzand continuing the reaction to completion. The excess carbonbisulphideis thereafter separated and the product filtered to removetraces oi insoluble heavy metal compounds. The desired sodiumthiocarbonate solution so obtained isjsubstantially free 'of sulphides.The reaction is carried out at any suitable temperature below therefluxing temperature of the mixture at the pressure employed as, forexample, from to 45 C. Temperatures of from to 40 C. are, however,enerally employed, and C. is the preferred ,reaction'temperature whenoperatingat atmospheric pressure Where-the reactionis carried out undersuperatmospherio pressure," somewhat higher temperatures maybe'e-m'ployed; if desired, I

A.-.m01ecular excess of carbon bisulphide with "respect to sodiu'msulphide hydrate isllrequired in the-reaction mixture The amount ofWater em-ployed -is not critical but influences the rate atwhich-Jthe-sodium sulphide hydrate is added" to athe reaction mixture.Thewminimum water required inthe reaction zone-varies withthe amount of:sodium sulphide hydrate present' and the degree ofhydration of thesodiumsulphide, and is that f amoun't whichw ill not be completely used up inethehformation :ofv higher and solid sodium sul- 'phid'I' hydrates.""While sodium hydroxide, and v15 .preferalblyxan' aqueouszsolutionthereof, is generallysused sin correcting .thepl-I .of the reaction.mixture following-the preliminary reaction :be- :tweehlxthe sodiumsulphide hydrate and carbon .bisulphide other water-soluble alkalinematerials :maiy".be:..employed,-xsuch .as sodium carbonate. .Suc'h:materials,-howev.er; do not always react .wit'hsithe z=soclium acidsulphide presentin the .reaction mixture andmay-be carried through.into: the finalproduct as impurities; The optimum pI-I to which themixture is adjusted prior ..to completion: of the reaction depends uponthe -..amount;of :water employed and on the concentra- .tion of ;thecrude .soidium .thiocarbonate .inthe' ireactionmixture. v.Where it i-isdesired to obtain asa finalproduct a concentrated solution having .'-.aspecific. gravityof 1.50101 higher .at 25 /4? 0.. and apI-Lrange :of 9.0to 9.6, as determined by a iglass electrode;-the:p'H of the partiallyreacted .mixturerisiadjusted to at least 8.0. The pH mayv .bG adjustedto higher valuesltwhen more dilute" solutions are involved. Any suitableequipment not attacked by the reaction'mixture may beemi.ployed,:.such.as glassline, .iron, .or nickel stills, I

and thelike; v40 aeln carryingiout the invention, all of the sodium*sulphide hydrate may be addedtothe carbon -bisulphide .and;a'-sui,table amount of water, the :mixture? partially. reacted, the pHadjustment :cmadeyaridthe reaction. completed, the mixture --beingthereafter treated in known manner to re- -move excess carbon-bisulphide'-' and water-insoluble metal salts. In actual-practice,=however, it is'generally'preferred to employa reduced amountof w'ater in mixture-with-the carbon'bisulphide,

and to add thesodium sulphide hydrate portion- Wise to this mixturein'such manner and amount that eaclfi portion of sodium sulphidehydrate, althoughit may be initially insoluble in the water present, isreacted with or' dispersedinthe reacis thereafter continued tocompletion, as determined by analysis of aliquot portions of .the

mixture, and the excess and unreacted carbon" bisulphide separated as bylayering off or by evaporation. The resulting product consists essen--tially in a water solution of sodium thiocarbonate which is filtered, ifdesired, to remove small amounts of impurities such as insoluble ironsalts and the like. The following example sets forth one embodi.-,. mentof our invention, but is not to be construed as limiting the same:

A mixture of 600 grams of carbon bisulphide, 300 grams of distilledwater, and 234 grams of a commercial sodium sulphide hydrate flakecontaining 10 per centby weight sodium bisulphide and 50 per cent sodiumsulphide in the form of mixed hydrates, were mixed together and agitatedin a glass-lined reactor equippedwitha reflux condenser at a temperaturejust below the reflux temperature of the mixture. As soon as the sodiumsulphide hydrate was. dispersed, an additional 233 grams thereof wasadded with mixing and the reaction continued until this also passed intothe solution. Another 233 gram portion of sodium sulphide hydrate wasthen added and the mixture agitated at a temperaturebelow the refluxtemperature and in the neighborhood of 3540 C. until no solid sodiumsulphide hydrate flake remained in suspension. 125 grams of 50 per centby weight aqueous sodium hydroxide was then poured slowly into thereaction mixture, this amount being suflicient to neutralize the sodiumbisulphide present and to adjust the pH of the mixture to approximately8.05, as determined with a glass electrode. Agitation at 35 C. wasthereafter continued for 24 hours, at the end of which time the excesscarbon bisulphide present in the reaction mixture was layered off andthe aqueous solution filtered through asbestos. The resultant solutionhad a pH of above 9.0, a specific gravity of 1.495 at 20 C., andcontained 55.85 per cent by weight of sodium thiocarbonate, 0.08 percent of sodium sulphide, 1.45 per cent of sodium carbonate, 0.68 percent of sodium thio sulphate, 0.29 per cent of sodium chloride, and41.65 per cent of water. This solution did'not burn or flash attemperatures below its boiling point of 120 C.

By varying the proportions of reactants or water shown in the foregoingexample and/or modifying the reaction conditions with respect totemperature, time and pH within the limits indicated, aqueous solutionsof sodium thiocarbonate may be obtained of varying percentagecomposition. In operating according to the invention, however, suchsolutions contain less than 1 per cent by weight of sodium sulphide orother watersoluble sulphides on the basis of sodiumqthiocarbonateproduced.

1. A method for the preparation of sodium thiocarbonate which comprisesthe steps of partially reacting sodium sulphide hydrate with a molecularexcess of carbon bisulphide in the presence of water, thereafter addingalkali in sufficient amount to adjust the pH of the reaction mixtureto'above 8.0, and continuing the reaction to completion.

. 2. In the preparation of sodium thiocarbonate .from sodium sulphidehydrate and a. molecular excess of carbon bisulphide in the presence ofwater, the steps which consist of adjusting the pH of a partiallyreactedmixture of the above ma- -ter'ials{to above 8.0 with alkali, andthereafter completing th e reaction by warming to a temperature notinexcess 'of the reflux temperature of the mixture atth'e pressureemployed.

um thiocarbonate solutions from sodium sulphide hydrate,'amolecularexcess of carbon bisulphide, and water in amount sufficient to dissolveall the sodium sulphide hydrate employed, comprising the steps of addingthe sodium sulphide hydrate portion-wise to a mixture of the carbonbisulphide and waterat a temperature not, in. excess of the refluxtemperature of the reaction mixture at the pressure employed, correctingthe pH of the partiallyyreacted mixture to about 8.0 with alkali,warming themixture to the reaction temperature for an additional periodsufficient to complete the reaction, and separating ,the excess carbonpartially; reacted mixture of the above materials suflicient sodiumhydroxide to adust the pH thereof to above.8.0, and thereaftercompleting the reaction by warming .to a temperature not in excess ofthe reflux temperature of the mixture at the pressure employed.

6. A method for the preparation of substantially sodium sulphide-freesodium thiocarbonate comprising the steps of mixing sodium sulphidehydrate with a molecular excess of carbon bisulphide in the presence ofwater at a temperature not in excess of the reflux temperature of themixture at the pressure employed, adding sodium hydroxide to the reactedmixture in amount sufficient to neutralize sodium acid sulphide presenttherein and to impart a pH of above 8.0 thereto,

and continuingthe reaction to completion.

7. A method for the preparation of concentrated and substantially sodiumsulphide-free sodium thiocarbonate solutions from sodium sulphidehydrate, a molecular excess of carbon bisulphide, and water in amountinsufficient to dissolve all of the sodium sulphide hydrate employed,comprising the steps of adding. the sodium sulphide hydrate portion-wiseto a mixture of the carbon bisulphide and water at a temperature not inexcess of the reflux temperatureof the reactionniixturewatthe pressureemployed, ad-

justing' the pH of .the partially reactedmixture to above 8.0 withaqueous sodium hydroxide, warming the mixture to the reactiontemperature for amount not in excess of 1 per cent by weight of anadditional period sufiicient to complete the redissolved sodiumthiocarbonate as prepared by action, and separating the excess carbonbisulthe method of claim 1. phide. SHELDON B. HEATH.

8. An aqueous solution of sodium thiocar- WALLIS R. BENNETT. 5 bonatecomprising water-soluble sulphides in

